This invention relates to a color video endoscope system, and in particular to an endoscope system having electronic color filtering to alter the true color of the image presented on the monitor.
Various color video endoscope systems are described in U.S. Pat. No. 4,253,447 to Moore and U.S. Pat. No. 4,074,306 to Kakinuma. Such systems include a control unit which generates alternating fields of red, green, and blue (RGB) light. The light is directed through a fiber optic light guide within a separate endoscope section which plugs into the control unit and which has a viewing head for insertion into the cavity to be viewed. The light reflected from the cavity into which the viewing head is inserted is received by a solid state image sensor in the viewing head. The image sensor transmits an electrical signal back to the control unit in response to the intensity of light reflected within the cavity from the sequential color fields. The signal is processed according to its separate red, green, and blue components by the control unit and then later merged into a composite RGB video signal compatible with a monitor.
In such color video endoscope systems it is often desirable or necessary to filter certain colors of the light. For example, fluorescein dye is often injected into a patient and absorbed by certain tissue. This particular dye is an excellent reflector of blue light so that if other colors are filtered out from the image on the monitor, the particular tissue under study will be emphasized. In another application of color filtering, it may desirable to give the appearance that the light within the cavity is incandescent light so that indoor film can be used to take a photograph of the image on the monitor. This effect can be accomplished by filtering out portions of the blue and green light in order to give an orange tint to the image. In still another application, it may be desirable to take a "polaroid" photograph of the image on the monitor, in which case it is necessary to slightly increase the blue light by reducing the amount of red and green light from the image.
In conventional color video endoscopes, color filtering is accomplished mechanically in various ways by altering the color of the light entering the cavity. For example, if it is desirable to create a blue image, then only blue light is directed through the fiber light guide and into the cavity by placing a blue filter in the light path. The conventional system of filtering light has several inherent disadvantages. First, because the light is filtered with optical color filters placed in front of the light source, only a discrete number of filter combinations are available. Thus, while it would be possible to utilize a blue filter so that only blue light entered the cavity, it would not be possible to select any particular shade or intensity of blue light. In addition, the filters are subject to damage and degradation by being placed for substantial periods of time in front of the light source.